As the number of wireless cellular data communication devices continues to increase and as their data capabilities continue to be more and more heavily used, the demands on available infrastructure and resources e.g. in the frequency domain continue to increase. The addition of infrastructure to meet this ever increasing demand is costly, and is becoming more and more difficult as unoccupied space suitable for placement of base stations diminishes. In addition, as saturation of available wireless communication frequencies approaches, addition of infrastructure approaches a point of ineffectiveness.
In order to support the ever increasing demand for data communication services, network operators are turning more and more towards increasing the efficiency of their operations. One mechanism that has shown promise is the use of active antenna systems (AAS) for base stations which can be employed for realizing a so called vertical sectorization (VS) of at least some of the cells of a cellular radio telecommunication network. AAS comprise radio antennas each having at least two antenna elements and an appropriate control entity.
In the case of transmitting, the radio signals are split up according to the number of antenna elements and the control entity is capable of adjusting the phase shift and the signal power individually for each antenna element in order to generate different beams for different radio signals such as different radio frequency (RF) drive signals, for different radio access technologies (RATs), or even for different intra-frequency cells as in case of vertical sectorization. Depending on the selected phase difference and the geometry and the relative spatial arrangement of the antenna elements the transmitted radio beam can be spatially directed towards a preferred region.
In the case of receiving, the control entity is capable of adjusting the phase shift and a sensitivity for receiving signal power individually for each antenna element in order to be sensitive for different radio beams. Thereby, the sensitivity for receiving radio signals which have been emitted by transmitters (e.g. radio communication end device or user equipments) being located within predetermined regions can be adapted.
Descriptive speaking, one significant benefit of AAS is the ability to control antenna parameters electronically, such as by changing azimuth and elevation patterns and steering radiated radio beams vertically and horizontally. Tilt control provided by AAS may be accomplished on a carrier basis, a frequency basis, or a service basis allowing flexibility for advanced network planning features such as VS.
Further, AAS are radio embedded base station antennas that integrate conventional base station RF components with the antenna elements. Such an approach has the direct effect of eliminating RF power losses in RF feeder cables and minimizing the number of hardware items which have to be implemented within a base station.
VS increases the number of cells beyond the number provided by conventional mechanisms, generally enabling two cells in the vertical plane per conventional cell sector. In general, the outer sector is optimized for cell coverage and the inner sector is adjusted in order to maximize network capacity. Thereby, two dedicated sectors are created which effectively doubles available resources over the area as a whole, thus significantly improving the performance of the respective cellular radio telecommunication network. VS also allows for directing dedicated resources to sector edges, thus improving outer sector coverage. In addition, VS can lower deployment and operational costs for operators by reducing the number of base station sites required.
In cells employing a VS the antenna tilts for inner and outer sectors should be selected in such a manner that the radio traffic load is more or less equally shared between the inner sector and the outer sector. Thereby, the radio traffic load can be measured through e.g. a determination of Transmission Time Interval (TTI) usage in the inner sector and the outer sector. On the other hand an overlap region area between the inner sector and the outer sector causes unfavorable interference in case of frequency reuse and should therefore be minimized. This holds in particular in case of a user concentration in that overlap area.
Correct antenna tilts are usually a compromise between increased number of resources per area and interference due to the additional cell border between the inner sector and the outer sector in particular in case of a so called co-channel deployment.
There may be a need for determining an optimized beam tilt setting for a base station providing flexible cell deployment which relies on the principles of a vertical sectorization (VS).